The invention relates to an apparatus for dispensing a so-called "paste" on the surface of a ceramic subtrate for forming a thick film integrated circuit. Such an apparatus is sometimes referred to as a direct writing machine. More particularly, the invention pertains to a method and apparatus for accurately positioning a dispensing nozzle such that accurate spacing between the dispensing nozzle and the subtrate is maintained.
There are many kinds of pastes for forming a thick film integrated circuit. For instance, there are electrically conductive natured pastes, non-conductive natured pastes, and resistive natured pastes. These pastes are typically charged separately into each nozzle. During dispensing, a nozzle tank with a nozzle at its bottom is attached to the circuit-forming-apparatus such that the paste is dispensed from the nozzle. When the paste tank is to be changed, the present tank with its nozzle attached thereto is removed from the apparatus and the new required nozzle tank with its nozzle is installed. Thus, a hybrid circuit may be formed.
During the dispensing process, the dimension between the nozzle and the subtrate is, for example, between 0.06mm and 0.08mm. To form the circuit smoothly, whenever the tank is changed, this dimension must be checked again.
Referring to FIG. 8, one conventional way of setting this dimension will be explained. FIG. 8 illustrates a sensor S, an X-Y table on which a subtrate is placed, a tank T, a nozzle N, a motor M, a rail R, and an up-down mover H driven by a motor M.
To position the nozzle at the predetermined height, firstly, the nozzle is lowered by the motor M along the rail R, until it touches the touch sensor S. Secondly, the nozzle N is moved horizontally to the X-Y table such that an accurate spacing dimension between the nozzle and the X-Y table is secured.
According to the prior art, when the nozzle N touches the sensor S, the paste sticks at the surface of sensor S. Thereby, it is hard to get an accurate positioning of the nozzle N. Besides, the sensor S is often damaged because it is located near the X-Y table Ta.
It is therefore an object of the invention to eliminate the aforementioned demerits.